Formula to give an average time for month

Good Evening

I am hoping this wont be to hard, I need a formula to be able to give me a monthly average off a row that shows total hh:mm:ss of line activity during a working day, I have attached an example workbook so you can see what I am trying to achieve, The basic formula is in BF9 however I have actually played with a lot of different formulas but had no joy so dont know if I have over complicated it or if there is some way of doing it

Many thanks

Dave